GB822532A - Improvements in method of curing polyurethane elastomers - Google Patents

Abstract

A method of curing a polyurethane elastomer having terminal unsaturation comprises compounding 100 parts by weight of such elastomer with from 0.25 to 10 parts of an organic peroxide, coating the resulting composition with a film of polyvinyl alcohol, and heating the assembly in air at a temperature of from about 50 DEG to about 100 DEG C. for a period of from 5 minutes to 24 hours. The term "polyurethane" is used to denote organic polyisocyanate modified polyesters, polyethers, polyester-ethers and polyester amides. A compound giving urea linkages, e.g. diamines, amino-alcohols or aminophenols, diamides or water may be present in the reaction mixture from which the polyurethanes are prepared. The unsaturation may be ethylenic or acetylenic. It may arise from the presence in the mixture of reactants from which the polyurethane is prepared of compounds which contain non-benzenoid unsaturation and but one grouping with active hydrogen, such as OH, NH, NH2, SH, COOH or CONH2. A number of such compounds is listed. Peroxides specified as suitable are benzoyl, acetyl, succinyl, acetyl benzoyl, cumyl, di-tertiary-butyl, di-t-amyl, t-butyl 1-methyl-cyclohexyl, and di-(3-methyl-pentynyl) - 3 - peroxides, t - butyl - hydroperoxide, 2,2 - bis - (tertiary - butyl - peroxy) - butane and 2,2 - bis - (t - butyl - peroxy) - propane. The peroxide may be incorporated with the polyurethane on a rubber mill (and fillers such as asbestos, blanc fixe, clay, iron oxide, lithopone, mica, silicious materials, titanium dioxide, whiting, flock, colouring matter and pigments may also be added) or in solution in such solvents as hydrocarbons, ethylene dichloride or ketones such as methyl ethyl ketone, ethyl isobutyl ketone or cyclohexanone, ethers, esters, dioxane or ethyl acetate. The solution may be used in coating the interior or exterior of tyres or to coat nylon, rayon or cotton to form a gasket. The composition may be calendered on to fabrics (suitably pretreated with a diisocyanate) to give a material for making fuel tanks. After shaping, the composition is coated with a solution of a polyvinyl alcohol, which preferably contains 10 to 30% of unhydrolysed acetyl groups. After drying, the assembly is heated in air, e.g. in an oven or autoclave, at 50 DEG to 200 DEG C. to effect curing, and the polyvinyl alcohol film may then be washed off. In examples, an hydroxypolyester is prepared from adipic acid and ethylene and propylene glycols. In (1) this is reacted with a mixture of 4,41-diphenylmethane diisocyanate and methallyl alcohol (diethylcyclohexylamine catalyst being added near the end), and bis-(anilino) methane is added and the reaction continued. The product is formed into a cement with dioxane and carbon black, and after adding dicumyl peroxide, dried films formed from the mixture are coated with polyvinyl alcohol and cured by heating in air at 285 DEG F. In Example (2) the polyester is reacted with a mixture of 2,4- and 2,6-toluene diisocyanates and methallyl alcohol, the product is reacted with bis-(anilino) methane, and the elastomer cured in the form of films by a process similar to Example (1), magnesium oxide being an additional ingredient of the final mixture. Specification 820,004 is referred to.